java - How to properly use load array and save array methods? -

i have following code designed user click on button , when click on button, particular string viewing favorited , stored somewhere else.

i have 2 questions.

1. one what's wrong have right now? crashes when click button.

2. how go finishing on load array method string loaded , saved array user see array later?

thanks time!!

fav.setonclicklistener(new view.onclicklistener() {          public void onclick(view v) {              loadarray("favorites");             favorites = arrays.copyof(favorites, favorites.length+1);             favorites[favorites.length]=display.gettext().tostring();             savearray(favorites, "favorites");          }     });      home.setonclicklistener(new view.onclicklistener() {          public void onclick(view v) {              intent openstartingpoint = new intent("starting.rt.menu2");             startactivity(openstartingpoint);         }     });      search.setonclicklistener(new view.onclicklistener() {          public void onclick(view v) {              intent openstartingpoint = new intent("starting.rt.search");             startactivity(openstartingpoint);         }     });      moreapps.setonclicklistener(new view.onclicklistener() {          public void onclick(view v) {              intent gotomarket;             gotomarket = new intent(intent.action_view, uri                     .parse("market://search?q=pub:\"wompa\""));             startactivity(gotomarket);         }     });  }  public string[] loadarray(string arrayname) {       sharedpreferences prefs = getsharedpreferences("preferencename", 0);       int size = prefs.getint(arrayname + "_size", 0);       string array[] = new string[size];       for(int i=0;i<size;i++)           array[i] = prefs.getstring(arrayname + "_" + i, null);       return array;   }    public boolean savearray(string[] array, string arrayname) {        sharedpreferences prefs = getsharedpreferences("preferencename", 0);       sharedpreferences.editor editor = prefs.edit();       editor.putint(arrayname +"_size", array.length);       for(int i=0;i<array.length;i++)           editor.putstring(arrayname + "_" + i, array[i]);       return editor.commit();   }  

log cat

05-08 23:10:51.329: i/process(495): sending signal. pid: 495 sig: 9 05-08 23:11:02.360: d/dalvikvm(504): gc_external_alloc freed 44k, 53% free 2553k/5379k, external 1625k/2137k, paused 221ms 05-08 23:11:08.599: d/dalvikvm(504): gc_external_alloc freed 16k, 51% free 2644k/5379k, external 2707k/3308k, paused 174ms 05-08 23:11:12.570: d/androidruntime(504): shutting down vm 05-08 23:11:12.570: w/dalvikvm(504): threadid=1: thread exiting uncaught exception (group=0x40015560) 05-08 23:11:12.599: e/androidruntime(504): fatal exception: main 05-08 23:11:12.599: e/androidruntime(504): java.lang.nullpointerexception 05-08 23:11:12.599: e/androidruntime(504):  @ starting.rt.base$1.onclick(base.java:52) 05-08 23:11:12.599: e/androidruntime(504):  @ android.view.view.performclick(view.java:2485) 05-08 23:11:12.599: e/androidruntime(504):  @ android.view.view$performclick.run(view.java:9080) 05-08 23:11:12.599: e/androidruntime(504):  @ android.os.handler.handlecallback(handler.java:587) 05-08 23:11:12.599: e/androidruntime(504):  @ android.os.handler.dispatchmessage(handler.java:92) 05-08 23:11:12.599: e/androidruntime(504):  @ android.os.looper.loop(looper.java:123) 05-08 23:11:12.599: e/androidruntime(504):  @ android.app.activitythread.main(activitythread.java:3683) 05-08 23:11:12.599: e/androidruntime(504):  @ java.lang.reflect.method.invokenative(native method) 05-08 23:11:12.599: e/androidruntime(504):  @ java.lang.reflect.method.invoke(method.java:507) 05-08 23:11:12.599: e/androidruntime(504):  @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:839) 05-08 23:11:12.599: e/androidruntime(504):  @ com.android.internal.os.zygoteinit.main(zygoteinit.java:597) 05-08 23:11:12.599: e/androidruntime(504):  @ dalvik.system.nativestart.main(native method) 05-08 23:11:17.869: i/process(504): sending signal. pid: 504 sig: 9 

loadarray function returns string[]. might want use like:

string [] arr = loadarray("favorites");   

this array can used later asked in 2nd part. hope helps.

update [based on comment]

so, if want grab text in textview , wish add in list/string array:

1) try string textview

textview display = (textview)findviewbyid(r.id.display); string tosave = display.gettext().tostring(); 

2) existing list sharedpreferences using `loadarray':

string [] arr = loadarray("favorites");   

3) add new string it:

arraylist<string> arrlist = new arraylist<string>();  (int i=0; i<arr.length(); i++) {      arrlist.add(arr[i]); //add old values arraylist } // add new string it:  arrlist.add(tosave);  //get array string [] array = arrlist.toarray(new string[arrlist.size()]);  

4) save again.

savearray(array, "favorites");